The way in which plants sense, transduce and integrate environmental and endogenous signals are crucial to plant growth and development. This project aims to investigate the crosstalk between light and metabolite signal transduction pathways using a molecular genetic approach in Arabidopsis. This will be carried out by focusing on transcriptional control of the asparagine synthetase gene, ASN1. ASN1 gene expression is activated in the dark and is repressed by light and carbon. This repression is antagonized by nitrogen in the form of amino acids. A mutagenized Arabidopsis line containing the AS1-GUS/AS1- HPH reporter gene will be used in a positive genetic screen to isolate light repression insensitive (lir) mutants. Lir mutants will further be screened to identify mutants which are light and carbon repression insensitive. Phenotypic characterization of lir mutants will identify defects in light, carbon and C:N sensing and signal transduction. Finally, disruptions in genome-wide expression patterns will be investigated in the lir mutants using DNA microarrays. This mutant isolation and characterization will be extremely informative as it aims to dissect the integration of light, carbon and nitrogen sensing and signal transduction pathways.